A vehicle's engine may be stopped when the vehicle stops to conserve fuel. If the vehicle's driver or controller requests torque, the engine may be restarted to provide motive force for the vehicle. In this way, fuel may be conserved when little torque is requested to propel the vehicle. However, frequently starting and stopping the vehicle's engine main increase the possibility of starter degradation. Further, if an amount of requested torque is increased while the engine is stopped, a significant delay period may transpire before torque is made available to meet the torque request. Another way to increase fuel economy during low torque demand conditions is to shift a transmission that is coupled to the engine into neutral. Shifting the transmission into neutral lowers the load that the transmission applies to the engine. However, if the driver requests an increase in engine torque, a driveline torque disturbance (e.g., a “clunk”) may be observed by the vehicle's occupants when the transmission is shifted back into gear. The “clunk” may be caused by clearances between transmission torque transferring components. For example, applying engine torque to the transmission may remove space between gear teeth (e.g., gear lash) which causes impact between gear teeth. It may be desirable to provide a way of conserving fuel during low torque demand conditions while reducing the possibility of disturbing vehicle occupants when additional torque is requested.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: shifting a transmission into neutral from a forward gear via a controller in response to vehicle speed being less than a threshold and a brake pedal being applied; and shifting the transmission into a forward gear via the controller in response to the brake pedal being released to a position within a threshold distance of top of brake pedal travel.
By shifting a transmission from neutral to a forward gear before a brake pedal is fully released, the technical result of reducing “clunk” and being ready for an increase in requested torque may be provided. In particular, shifting from neutral to a forward gear while the brake pedal is partially applied may prevent space between gear sets from opening so that impact between gear sets during shifting may be reduced. Further, the brake pedal position may be used as an indicator of an impending vehicle launch so that the transmission may be engaged in a forward gear at the time an increase in torque is requested. As a result, engine torque may be delivered to vehicle wheels through the transmission almost as soon as it is requested. In addition, situational awareness sensors and paddle shifting switches may also provide information that indicates an impending increase in engine torque. The transmission may also be shifted from neutral to a forward gear based on these inputs.
The present description may provide several advantages. In particular, the approach may reduce driveline torque disturbances. Further, the approach may improve vehicle drivability and fuel economy. Additionally, the approach may provide driving options that heretofore have not been available.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.